1. Field of the Invention
This invention concerns a laboratory stirrer which includes a synchronous motor for driving a stirring rod.
2. Description of the Prior Art
A controlled temperature is an essential requirement for all tissue and cell culture in vitro and in cell suspension culture (widely used in cancer research). The media used as liquids for suspension cell culture range from horse serum to embryo extract to protein-free media. Most workers have gassed the culture with air containing 5% carbon dioxide. It is also necessary to be able to standardized the conditions of stirring. To do this there are several types of stirring apparatus which are well known to those of ordinary skill in the art.
One of the most common forms of stirring equipment is the magnetic stirrer. A typical magnetic stirrer comprises a plastic clad permanent bar magnet which is placed in the laboratory beaker and a base unit which produces a rotating magnetic field. The laboratory flask is placed upon the base unit and when the device is turned on, the permanent magnet is induced to whirl around inside the container. Unfortunately, such an approach has several drawbacks when used in the type of research outlined above. To avoid damaging the cells the rotating bar magnet has to be suspended clear of the base of the vessel and the bearings required eventually become clogged. Another drawback of conventional magnetic stirrers is that they generate a great deal of heat. It is generally desirable to maintain cell suspension cultures at a temperature between 35.degree. C. and 36.degree. C. Because magnetic stirrers create enough heat to unbalance certain sensitive cultures it is often necessary to provide heat shielding or refrigeration or both. Another disadvantage of such magnetic stirrers is that they cannot be immersed in a water bath.
In order to minimize the problems caused by heat and grinding this inventor had developed pneumatic equipment as described in U.S. Pat. No. 3,998,435 entitled "Oscillating Stirrers" and issued on Dec. 21, 1976. That device consists of three flexible diaphragms actuated by three phase alternating air (the analog of alternating electric current). These diaphragms are linked to a stirring rod and cause it to orbit and stir the culture medium. The following references were cited during the prosecution of U.S. Pat. Nos. 3,993,435: 3,332,669 issued July 1967 to Calonna; 3,484,204 issued December 1969 to Caviness; 3,913,895 issued October 1975 to Norman Adrian de Bruyne and 3,955,802 issued May 1976 to Norman Adrian de Bruyne.
Such pneumatic stirrers have several advantages. For example it is possible to put a pneumatic stirrer in a water bath. Conventional pneumatic stirrers using air motors cause problems because they discharge air to the atmosphere and hence cannot be used in incubators with a controlled carbon dioxide content. In contrast the inventor's pneumatic stirrer is a closed reciprocating device which entails no input or output of air to the atmosphere.
There are devices known to those of ordinary skill in the art for transmitting orbital motion into a vacuum vessel. See for example, FIG. 121 of Max Pollermann's "Bauelemente der Physikalische Technik" which discloses a nutating device for that purpose.